I did a search on this but couldn't find a thread about it.

How can you tell the difference between a legit authentic CD-game and a bootleg?

I guess the most important aspect is the non-label side. The current systems have imprints on the inner circle of the CD, but I'm lost when it comes to Playstation 1 and Dreamcast games.

Dreamcast games have more than this IFPI number printed on it, but I can't tell what exactly has to be printed on a CD to make sure it's legit; even worse are the PS1 games which have just a small IFPI number, but sometimes not. (and I'm sure I bought some of the games new from reputable established stores)

It would be also interesting to know the tell-tale signs of bootlegs and authentic games for other console disc systems as well.